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Ok, first of all, I know there are some on the forum that have built these motors and my hat is off to you. Let me start by saying, I have the greatest respect for those who take the risk to build something unique. My question is more related to the fact that there are things I don't understand about the motors and why to build them. Please set the record straight!

My understanding of the Frankenmotor is that you start off with the shortblock of a 2.5L engine, then add the cylinder heads from usually a 2.2L SOHC engine.

What I am wondering is, if you are going to the trouble of rebuilding the shortblock of a 2.5 engine why change the heads? Is it because the 2.5d engines have 2 cams each and it is cheaper to buy 1 reground cam per head than 2? Does no one make a reground 2.5d cam? Is there some other benefit to the 2.2 head over the 2.5d?

Another question, If I were to put a frankenmotor into one of my wagons, will the factory computer work? Both of my wagons have auto trans and EGR. Would I keep the 2.5 intake?

How do you select a good 2.5 core to re-build? Often times it is difficult to know the history of a junkyard motor. As many know these motors are prone to headgasket failure and subsequent overheating, which can lead to warpage and potential bearing failures.

All of the ej series subarus I have owned have been 2.5L engines, the first 3 have/had the 2.5d, my '02 OB has 2.5 sohc.

I am considering building a frankenmotor for future use in one of my wagons.

To answer the first part of your question. The reason of this engine is POWER!
The 2.2 heads on the 2.5 block raises the compression causing the engine to put out more power. Then reground cams and free flowing exhaust do their part to help as well.
Most people run a stock computer with it. But like any EFI system, more power can always be obtained by a custom tune.

Picking a good block without hearing it run is a crap shoot. And even then, you don't ever really know. But this is the same story with any engine. There is no way to tell without tearing it down and inspecting it. And then you might as well rebuild it.
CCR sells rebuilt 2.5 shortblocks for a good price from what I understand, and they seem to be the leader in quality and precision for rebuilt Subaru engines.

A DIY rebuild is gonna run $700 - $1000 for stock spec. Having a shop clean, mill, and hone the block is a few hundred usually, another couple hundred or so to have a set of heads reworked.

1. The compression increase is the biggest reason. Increases thermal efficiency and that is effective for making power.

2. 25D heads are about $500 to have rebuilt. Then cams are about $450 or so on top of that. Port/polish work can runs hundreds more - without increasing the comp. You might gain as much as the 22 heads if you have about $1500 to drop on just your heads.

3. You use the 25D gaskets. Gasket must match the cylinder bore.

4. You continue to use the cheap 22 timing belt setup.

5. You must run 91 octane or better. Same as a turbo.

The goal of the frankenmotor is cheap power - rebuilding the 25D block is not typically done as it will increase the cost. Often you can find cast-off blocks from people building EJ257 turbos using the EJ25D heads. I just got a nice short block for $100. I paid another $100 for a 97 EJ22 with a rod knock. I will do a light hone, new rings and bearings plus the torque cams..... probably be into it about $500. See how this works? You can't build an EJ25D for anything comparable. Plus I like the simplicity of the EJ22 heads with their easily adjusted valves, etc. It's just a great combo all around.

I've been looking for dyno info about one of these motors for a while. I read through pages and pages on NASIOC, and here, and didn't find much. One reported test on NASIOC put a franken-motor 2.5 block, 2.2 heads, with delta torque cams at 125whp. No mention of torque though. That was about it. Some people talked about getting theirs dynoed, but I never could find any threads about them actually following though.

If you find anything else about them post it up. I think there are a few others on this board interested as well.

If neither block has been overheated, either one should do fine. I'd do compression tests on both and pick the better of the two.

My understanding of the Frankenmotor is that you start off with the shortblock of a 2.5L engine, then add the cylinder heads from usually a 2.2L SOHC engine.

I can't be totally sure, but it looks like your confusion comes from this part^^^.

Frankenmotors are for people who already have an EJ22 in their car. You don't add the heads of an EJ22 because you'd already have those. You're just slipping in a different block. That block is bigger and gives you higher compression.

The (or one of the) godfathers of the Frankenmotor says to not add EJ22 heads if you already have an EJ25 in your car. It sounds like you do, so the Frankenmotor is not intended for you. You already have the bigger displacement that the Frankenmotor builders are seeking. Your heads also flow better. Apparently the increased compression of adding EJ22 heads does not outweigh the loss of flow.

There is a good reason to ditch the EJ25D heads even if you already have them - basically it comes down to cost and ease of maintenance. It is orders of magnitude cheaper to rebuild, add cams, and maintain (valve adjust, spark plugs, etc) the SOHC heads. For that reason alone it os a great option for some of us who dont want to spend $1500 on *just* head work to get the same low-end grunt as the 22E heads and maybea little better top-end...... which a lot of us don't care about anyway.

There is a good reason to ditch the EJ25D heads even if you already have them - basically it comes down to cost and ease of maintenance. It is orders of magnitude cheaper to rebuild, add cams, and maintain (valve adjust, spark plugs, etc) the SOHC heads. For that reason alone it os a great option for some of us who dont want to spend $1500 on *just* head work to get the same low-end grunt as the 22E heads and maybea little better top-end...... which a lot of us don't care about anyway.

GD

Well, you know I'm still on the fence on this one. I don't know the price or the performance gains from cams on an EJ25D, and I don't wanna know, because I'm happy with my Frankenmotor:)

Jacob, next time I'm out at Ricks, you need to take me for a ride in that beast!

Yeah, sure thing, as long as it's drivable. I have a few upgrades planned for the winter:cool:

The compression increase is what gives the power gain (HP but especially torque) as it improves the thermal efficiency of the engine. The head change is what does this - to increase the compression using the stock heads would take a piston replacement which would drive up the cost significantly and destroy the whole "cheap power" concept. The whole idea of the frankenmotor is that it can make close to 200 HP without spending more than about $800 in parts and machine work. You can't even buy a replacement (used, stock) EJ25D for that little.

I agree that if cost is no object then the 25D heads are the better choice but my experience is that you aren't going to build a 25D with the same grunt as the Frankenmotor for less than a couple thousand $. That is a large difference.

The compression increase is what gives the power gain (HP but especially torque) as it improves the thermal efficiency of the engine. The head change is what does this - to increase the compression using the stock heads would take a piston replacement which would drive up the cost significantly and destroy the whole "cheap power" concept. The whole idea of the frankenmotor is that it can make close to 200 HP without spending more than about $800 in parts and machine work. You can't even buy a replacement (used, stock) EJ25D for that little.

I agree that if cost is no object then the 25D heads are the better choice but my experience is that you aren't going to build a 25D with the same grunt as the Frankenmotor for less than a couple thousand $. That is a large difference.

GD

I see your point, and like I said, the Frankenmotor worked for me. At least we can hopefully agree that if you spend any money on performance things for an EJ22 without doing cams, then you're retarded.

I'm basing my on-the-fence-ness on what the Frankenmotor godfather says. Also, can't you just run a thinner head gasket to up the compression?

Nor is there any cost comparison on the cam pricing or "bolt ons" for the 25D. Obviously there are twice as many cams and what bolt-ons? wouldn't most of them be applicable to the frankenmotor as well?

Good points but more data is needed. I still highly doubt you could get the performance from the 25D as cheaply by using the DOHC heads. A rebuild on the DOHC heads runs me about $500 vs. $160 for the SOHC heads........ at least double the price for cams - you are near $1000 right there.

Yes, you can frankenmotor an EA82. In order to do that, you'll need an EJ to EA adapter plate (obtainable from SJR, possibly others as well) and an EJ donor car. You'll need the engine harness and ECU out of the donor car to make it all work. And, as with all such swaps, there is likely to be a number of little odds and ends you'll want from the donor as well.